1. Field of Invention
This invention relates to methods of protecting plants from plant parasitic nematodes and more particularly to such methods using a synergistic combination of compounds.
2. Prior Art
Plant-parasitic nematodes are unsegmented worms, largely under one-eighth of an inch in length. Most species occur in soil and many of them attack the roots and other underground parts of plants. Some, on the other hand, attack the crown, stem, leaves, buds or seeds of plants.
Plant-parasitic nematodes damage crops and reduce yields of useful produce in several ways. Some species, termed "ectoparasites," attack plants largely from the outside. Their feeding often results in the death of the rootlets involved. When the numbers of such nematodes are large, many rootlets are killed, and crops suffer by correspondingly reduced growth and limited yields. Other species, termed "endoparasites," enter and live within the root tissue. Both ectoparasitic and endoparasitic nematodes may cause the death of the tissue surrounding the point of attack as well as malformation of the plant part involved. Such effects not only reduce the general vigor of the plant, but, in many cases, actually destroy the market value of the produce (such as malformed carrots). Furthermore, damage caused by plant-parasitic nematodes may serve as entry points for other plant pathogens such as fungi, bacteria and viruses.
Crop losses in the United States alone due to plant-parasitic nematodes are estimated to be in the range of one-half to one billion dollars annually.
The two basic methods available for avoiding or mitigating nematode damage to crops are to increase fertilizer and water to offset stunted root systems or to apply chemicals to control the nematodes. The first method is expensive and only partially effective, especially when the nematode causes malformation of the produce. The second method, while more effective, has been hampered by the lack of suitable chemicals. Many of the chemicals now available for nematode control are exceedingly phytotoxic and therefore unsuitable for use on growing crops. Others are unpleasant to handle, temporary in action or excessively expensive.